1. Field of the Invention
The present invention relates to a navigation system for a vehicle, such as vehicle.
2. Description of the Related Art
Recently, there has been developed a delivery service to deliver the map information to users by means of an internet system. In the field of navigation system, a study to obtain the map information for a user""s object through such a delivery service for map information is being carried out.
Japanese Patent Application Laid-open No. 2000-251196 discloses a system where the positional information guiding a route from the starting point to a user""s destination is transmitted to a server that delivers the map information to users via an internet. Subsequently, the corresponding map information is delivered (down-load) from the server to the user""s navigation system.
Japanese Patent Application Laid-open No. 2001-82965 discloses another system where the positional information of a vehicle (e.g. user""s vehicle) is transmitted to the server and then, a predetermined area of map information corresponding to the positional information is returned to the user.
Thus, in common with the above systems utilizing the map information loaded from the server, it is unnecessary to possess the map information in advance and is possible to utilize a brand-new map information anytime.
In the former system (No. 2000-251196), however, a problem of impossibility to gain the map information will arise unless the guidance route is determined.
In the latter system (No. 2001-82965), since the server delivers only the map information corresponding to the present position of the vehicle, a problem arises when a further movement of the vehicle requires a new map information. In detail, if it is started to gain the next map information when the vehicle goes out of the area of a map on display, there is produced a state of vacant display (map vacuum) because it takes much time to collate the user""s code number with the server""s code number, including the delivery of new map information.
In order to solve the above problems, it is supposed that the server delivers the map at regular intervals. However, if the vehicle moves slower than an estimated speed, then the map information having overlapped areas is transmitted to the user excessively, causing a rental fee about the map information to be elevated.
Under the above circumstance, it is an object of the present invention to provide a navigation system which allows the map information to be delivered (down-load) to a user in appropriate time with the moving situation of a vehicle.
According to the present invention, the above-mentioned object is accomplished by a navigation system for a vehicle, comprising:
a communication unit connected to a server for delivering a map information;
a map gaining unit connected to the communication unit thereby to gain the map information from the server through the communication unit;
a display unit connected to the map gaining unit thereby to display the map information gained by the map gaining unit, in the form of a map image;
a position detecting unit for detecting the position of the vehicle;
a renewal time calculating unit for calculating a renewal time necessary to renew the map, the renewal time including a time for gaining the map information;
a moving distance calculating unit for calculating a moving distance of the vehicle traveling during the renewal of the map;
a road distance calculating unit for calculating a road distance required for the vehicle to travel from its present position to a margin of the map displayed on the display unit;
a comparing unit for comparing the road distance with the moving distance; and
an extraction-area setting unit for establishing the area of a new map to be displayed next to the map presently displayed on the display unit when the road distance agrees with the moving distance;
wherein the map gaining unit transmits information about the area of the new map established by the extraction-area setting unit, to the server through the communication unit and further gains a new map information from the server thereby to carry out the renewal of the map displayed on the display unit.